Solid-state image pickup apparatus for reading out image signals with pixels reduced in a horizontal direction and a signal reading method for the same

ABSTRACT

A solid-state image pickup apparatus includes a color filter having an R (red), G (green) and B (blue) vertical stripe pattern. During preliminary pickup, a signal feeding section feeds particular drive signals for reading signal charges out of only odd-numbered columns or even-numbered columns. As a result, the signal charges or image data reduced to, e.g., one-half in the horizontal direction are transferred along a horizontal transfer path. The signal feeding section feeds horizontal drive signals adjusted in timing to the horizontal transfer path, causing the above image data to be read out without varying reading frequency. This doubles the horizontal transfer rate to thereby improve the signal output rate during preliminary pickup despite high pixel density, and allows signals to be read out without effecting actual pickup to follow.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a solid-state image pickup apparatusfor reading out image signals with pixels reduced in a horizontaldirection, and a signal reading method for the same. The presentinvention is advantageously applicable to, e.g., a digital camera or animage input apparatus including an image pickup section having highpixel density.

2. Description of the Background Art

To implement image quality comparable with one available with a silverhalide photo-sensitive type of film, there have been proposed varioustechnologies for increasing the number of pixels of a digital camerathat electrically shoots a scene. Japanese patent laid-open publicationNo. 136391/1998 discloses a solid-state image pickup apparatusconstructed to optimize the spatial sampling of an image, to shiftpixels with respect to each other in such a manner as to enhanceefficient receipt of light, and to reduce moiré and other aliasingsignals.

A digital camera of the type including an image pickup section providedwith high pixel density is extensively used and directed toward highimage quality. It is a common practice with this type of digital camerato effect, before the actual pickup of a still picture, AE/AF (AutomaticExposure/Automatic Focusing) operation and movie drive that causes ascene being picked up to appear on an LCD (Liquid Crystal Display).This, however, brings about a problem that the high pixel densityincreases the period of time necessary for signal charges resulting fromthe pickup to be read out and thereby lowers the frame rate. It is to benoted that the high pixel density refers to more than 1,000,000 pixelsor so-called megapixels.

To increase the frame rate, signal charges generated in the image pickupsection may be read out while being reduced, or thinned, in the verticaldirection. Specifically, assume that drive frequency CLK for reading outall of 1,500,000 pixels (1,280×1,024) by progressive scanning is 12.2725MHZ. Then, a single horizontal synchronizing period (1 H) and a singlevertical synchronizing period (1V) are 1,560 CLK and 1,050 H,respectively. The frame rate is therefore 1/7.5 second. When the signalcharges are reduced to one-half in the vertical direction, 1 H needs thesame period of time while 1V is 525 H, resulting in a frame rate of 66.7milliseconds, i.e., 1/15 second. Even when the signal charges arereduced to one-fourth in the vertical direction, 1V is 262.6 H, andtherefore the frame rate is as long as 33.4 millisecond or 1/30 second.

Assume that 1,500,000 pixels are read out by progressive scanning anddisplayed by the movie drive in the conventional image size, i.e.,640×480. Then, the pixels are reduced to one-half in the horizontal andvertical directions under the above-described conditions. As a result,the number of pixels in the horizontal direction and the number ofpixels (lines) in the vertical direction are as great as 640 and 525,respectively. Even the reduction to one-fourth implements only thereduction to one-half in the horizontal direction although reducing thenumber of pixels in the vertical direction to 262.5, i.e., improving theframe rate. However, because the number of pixels reduced in thevertical direction is short of 480, interpolation must be executed inthe vertical direction in order to match the number of pixels to thedesired number. On the other hand, in the horizontal direction, all ofthe 1,280 pixels are read out and then reduced to 640 pixels at thesubsequent signal processing stage. It will therefore be seen thatstrict consideration is not given to the improvement in frame rate inreducing the pixels in the horizontal direction. This is apt to preventthe operator of the camera to miss an adequate actual pickup timing.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide asolid-state image pickup apparatus capable of improving the signaloutput rate during preliminary pickup despite high pixel density orimage quality and reading out signals without effecting actual pickup tofollow, and a signal reading method for the same.

A solid-state image pickup apparatus of the present invention includesan image pickup section and a signal feeding section. The image pickupsection includes photosensitive cells arranged bidimensionally and eachbeing shifted from the adjoining photosensitive cells in the horizontaland vertical directions for photoelectrically transducing incidentlight. A color filter having R (red), G (green) and B (blue) colorfilter segments each are positioned in front of a particularphotosensitive cell in the direction of light incidence for separatingcolors of incident light representative of a scene. The R, G and B colorfilter segments each are arranged in a vertical stripe pattern. Transferelectrodes each are assigned to a particular photosensitive cell forreading out a signal charge generated by the photosensitive cell. Theapparatus sequentially performs preliminary pickup and actual pickup,which reads all of the signal charges out of the photosensitive cells,and executes digital signal processing with the resulting signals. Thesignal feeding section feeds transfer timing signals for transferringthe signal charges generated by only part of the photosensitive cellsarranged on odd-numbered columns or even-numbered columns to verticaltransfer paths via the transfer electrodes associated with the abovephotosensitive cells. Also, the signal feeding section feeds verticaldrive signals for transferring the signal charges along the verticaltransfer paths toward a horizontal transfer path perpendicular to thevertical transfer paths. Further, the signal feeding section outputshorizontal drive signals adjusted in timing for transferring the signalcharges along the horizontal transfer path while maintaining the colorof the individual signal charge.

A signal reading method applicable to the solid-state image pickupapparatus is also disclosed.

BRIEF DESCRIPTION OF THE DRAWINGS

The objects and features of the present invention will become moreapparent from the consideration of the following detailed descriptiontaken in conjunction with the accompanying drawings in which:

FIG. 1 is a block diagram schematically showing a solid-state imagepickup apparatus embodying the present invention and implemented as adigital still camera;

FIGS. 2A and 2B are schematic views showing the photosensitive array ofan image pickup section included in the illustrative embodiment, as seenfrom the light incidence side, together with a relation between signalcharges transferred in the horizontal direction and a relation betweenhorizontal drive signals;

FIG. 3 is a view showing the phases of the horizontal drive signals andthe shifting of potential wells formed by the drive signals;

FIGS. 4A and 4B are schematic views showing the photosensitive array ofan image pickup section included in a digital still camera, as seen fromthe light incidence side, together with a relation between signalcharges transferred in the horizontal direction and a relation betweenhorizontal drive signals; and

FIG. 5 is a view showing the phases of the horizontal drive signalsshown in FIG. 4B and the shifting of potential wells formed by the drivesignals.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIG. 1 of the drawings, a solid-state image pickupapparatus embodying the present invention is shown and implemented as adigital still camera 10 by way of example. Part of the digital stillcamera 10 not relevant to the understanding of the present invention isnot shown or described. In FIG. 1, signals are designated by thereference numerals attached to signal lines on which they appear. Asshown, the camera 10 includes a lens system 12, an operation panel 14, asystem controller 18, a signal generator 20, a timing signal feedingsection 22, a diaphragm adjusting mechanism 24, an optical low-passfilter 26, and a color filter 28. The camera 10 further includes animage pickup device 30, a preprocessing circuit 32, an ADC(Analog-to-Digital Converter) 34, a signal processor 36, acompression/expansion circuit 38, a record/reproduction circuit 40, anda monitor 42.

The lens system 12 is an assembly of a plurality of optical lenses andincludes a zoom mechanism and an AF control mechanism although not shownspecifically. The zoom mechanism controls the positions of the lensesand therefore the angle of field in response to a signal 14 a outputfrom the operation panel 14. The AF control mechanism automaticallycontrols the focus on the basis of the distance from the camera 10 to adesired subject. The operation panel 14 includes a shutter releasebutton, not shown, capable of being pressed to its half-stroke positionand then to its full-stroke position. When the operator of the camera 10presses the shutter release button to, e.g., the half-stroke position,the camera 10 preliminarily picks up a scene (preliminary pickuphereinafter) before actual pickup. The zoom mechanism and AF mechanismare controlled in accordance with information derived from thepreliminary pickup. The signal 14 a is also delivered to the systemcontroller 18 over a system bus 16.

The timing signal feeding section 22 is made up of a timing signalgenerator 22 a and a driver 22 b. A drive signal 22 c is fed to the lenssystem 12 via the signal generator 20, the timing signal generator 22 a,and driver 22 b. After the focus, exposure and so forth have been set onthe basis of the information derived from the preliminary pickup, theoperator presses the shutter release button to the full-stroke positionin order to actually shoot the scene. The resulting pickup timing is fedto the system controller 18. In response, the system controller 18executes pickup control including the image pickup and signal read-out.

The operation panel 14 allows the operator to select desired one ofitems that may be displayed on the monitor 42. The release shutterbutton sends the signal 14 a to the system controller 18 on the systembus 16 such that the camera 10 operates in a particular manner inaccordance with each of the half-stroke and full-stroke positions of theshutter release button. In the illustrative embodiment, the operationpanel 14 additionally includes a pointing device for indicating a cursoror a menu to be displayed on the monitor 42. The pointing device allowsthe operator to select desired modes in the event of various kinds ofoperation and processing. The signal 14 a input to the system controller18 is representative of various signals resulting from such functionsavailable with the operation panel 14.

The system controller 18 includes, e.g., a CPU (Central Processing Unit)and a ROM (Read Only Memory) storing programs for operating the camera10. The controller 18 generates control signals 18 a meant for thevarious sections of the camera 10 in accordance with, e.g., informationderived from the manipulation of the operation panel 14 and the programsstored in the ROM. Specifically, the control signals 18 a are deliverednot only to the signal generator 20 but also to the timing signal feedsection 22, preprocessing circuit 32, ADC 34, signal processor 36,compression/expansion circuit 38, record/reproduction circuit 40, andmonitor 42. Signal lines extending from the controller 18 to the blocks22 and 32 through 42 are not shown in FIG. 1. While controlling theabove various blocks, the controller 18 causes the timing signal feedingsection 22 to generate particular timing signals for each of preliminarypickup and actual pickup on the bus 16. Further, the controller 18executes unique control over the signal processor 36, as will bedescribed specifically later.

The signal generator 20 includes an oscillator, not shown, forgenerating a system clock 20 a under the control of the systemcontroller 18. The system clock 20 a is fed to the timing signal feedsection 22 and signal processor 36. Also, the system clock 20 a isapplied to the system controller 18 on, e.g., the system bus 16 as areference timing signal.

In the timing signal feeding section 22, the timing signal generator 22a includes a circuit for transforming, based on the control signal 18 a,the system clock 20 a to timing signals 22 d used to control the varioussections of the camera 10. The timing signals 22 d include transfershift gate pulses, vertical transfer timing signals, and horizontaltransfer timing signals. Generally, each timing signal 22 d is fed at aparticular timing and provided with a particular frequency for each ofpreliminary pickup and actual pickup. For preliminary pickup, however,each timing signal 22 d basically is not varied in frequency and is fedat a timing different from the timing assigned to actual pickup.

The image pickup device 30 includes photodiodes or photosensitive cellsand transfer shift gates or transfer electrodes adjoining thephotodiodes, as will be described specifically later with reference toFIGS. 2A and 2B. To vary the timings of the timing signals 22 d,transfer gate pulses to be applied to the transfer shift gates aregenerated and selectively fed to odd-numbered columns or even-numberedcolumns field by field. The vertical transfer timing signals causesignals charges read out of the photodiodes to be transferred alongvertical transfer paths and are generated in the conventional manner.The signal charges are then transferred along a horizontal transferpath. Paying attention to the positional relation between signals, thehorizontal transfer path of the illustrative embodiment has fourtransfer packets (see FIGS. 2A and 2B) in contrast to two transferpackets customarily assigned to actual pickup (see FIGS. 4A and 4B).Stated another way, the transfer electrode structure of the illustrativeembodiment deals with electrodes two times as great in number as theelectrode structure when a signal charge is present. In the illustrativeembodiment, the timing signal generator 22 a generates horizontaltransfer timing signals that allow a signal charge to move over theabove two times greater number of packets or electrodes whilemaintaining the original drive phase. This configuration will bedescribed more specifically later.

Basically, the timing signal generator 22 a generates the timing signals22 d and timing signals 22 e under the control of the system controller18 in accordance with pickup modes selected by the operator. The timingsignals 22 d and 22 e are respectively delivered to the driver 22 b andvarious sections of the camera 10, as shown in FIG. 1. The driver 22 bsuperposes the various timing signals to thereby generate drive signals22 c. The drive signals 22 c are fed not only to the zoom controlmechanism and AF control mechanism included in the lens system 12, butalso to the diaphragm control 24 and image pickup device 30. The driver22 b may also be directly controlled by the system controller 18.

In the illustrative embodiment, the system controller 18 also controlsthe signal 22 c used to read out signal charges at the time of actualpickup, although not described specifically. Briefly, the controller 18causes, in accordance with switching control, the timing signalgenerator 22 a to feed the field shift gate pulses only to odd-numberedcolumns or even-numbered columns field by field. Alternatively, thecontroller 18 may inhibit the driver 22 b from superposing the fieldshift gate pulses on the drive signal 22 c to be applied to the columnswhose signal charges should not be read out. For horizontal drive, useis made of a frequency low enough to read out signal charges at a lowrate during preliminary pickup. This successfully prevents the colors ofan image to be mixed together.

The diaphragm control mechanism 24 controls the sectional area of anincident beam, i.e., a lens opening such that an optimal beam isincident to the image pickup device 30. The driver 22 b feeds the drivesignal 22 c to the diaphragm control mechanism 24 also. The drive signal22 c causes the mechanism 24 to operate under the control of the systemcontroller 18. The system controller 18 calculates a lens opening and anexposure time on the basis of signal charges output from the imagepickup device 30 (AE processing), although not shown specifically.Control signals 18 a representative of the calculated lens opening andexposure time are input to the timing signal generator 22 a. Inresponse, the timing signal generator 22 a feeds the timing signal 22 dto the driver 22 b and causes it to deliver the corresponding drivesignal 22 c to the diaphragm control mechanism 24.

The image pickup device 30 has the previously mentioned photodiodes, orphotosensitive cells, arranged in a plane perpendicular to the opticalaxis of the lens system 12. The optical low-pass filter 26 and colorfilter are integrally arranged in front of the photodiodes in thedirection of light incidence. The low-pass filter 26 limits the spatialfrequency of an optical image to below the Nyquist frequency. The colorfilter 28 has filter segments corresponding one-to-one to thephotodiodes and effects color separation. In the illustrativeembodiment, the color filter is implemented by a single plate. Theconfiguration of the image pickup device 30, including the color filter,will be described more specifically later.

The image pickup device 30 may be implemented by a CCD (Charge CoupledDevice) image sensor or a MOS (Metal Oxide Semiconductor) image sensorby way of example. The image pickup device 30 is adapted to read outsignal charges generated by the photodiodes in a particular manner inthe preliminary pickup mode and actual pickup mode. The signal chargesare fed from the image pickup device 30 to the preprocessing circuit 32.

In the illustrative embodiment, the color filter has a so-calledhoneycomb arrangement and has R (red), G (green) and B (blue) colorfilter segments each being arranged in a vertical stripe pattern (RGBstripe pattern hereinafter).

The preprocessing circuit 32 includes a CDS (Correlated Double Sampling)circuit not shown. In the case where the image pickup device 30 isimplemented by a CCD image sensor, the CDS circuit includes a clampcircuit and a sample and hold circuit. The clamp circuit clamps variouskinds of noise ascribable to the image sensor in synchronism with atiming signal 22 e output from the timing signal generator 22 a. Thesample and hold circuit samples and holds the signal charges insynchronism with the timing signal 22 e. The CDS circuit delivers theresulting noise-free signals 32 a to the ADC 34.

The ADC 34 quantizes the signal levels of the analog signals, or signalcharges, 32 a by use of a preselected quantizing level and therebyconverts them to digital signals 34 a. The ADC 34 delivers the digitalsignals 34 a to the signal processor 36 in synchronism with a conversiontiming clock or similar timing signal 22 e output from the timing signalgenerator 22 a.

The signal processor 36 includes a data correcting circuit, a luminancedata generator, a luminance data interpolator, a high resolution, planeinterpolator and a matrix processing circuit although not shownspecifically. With these circuits, the signal processor 36 furtherenhances the quality of an image. The data correcting circuit includes agamma correction circuit for color correction and an AWB (AutomaticWhite Balance) circuit for automatic white balance control. The gammacorrection circuit uses lookup tables listing a plurality of sets ofdata, i.e., digital signals to be input to a ROM and correction data tobe output in accordance with the digital signals. While the datacorrecting circuit may be included in circuitry following the signalprocessor 36, it should preferably be included in the signal processor36 in order to minimize the number of lookup tables. Such datacorrection is also effected in synchronism with a timing signal outputfrom the timing signal generator 22 a. The data correcting circuitdelivers the correction data to the luminance data generator.

The luminance data generator operates under the control of the systemcontroller 18. For example, this data generator weights the correctiondata in consideration of the arrangement of colors to thereby generateluminance data Y for pixels where the photodiodes are positioned. Theluminance data Y are fed to the luminance data interpolator. Theluminance data interpolator interpolates luminance data in virtualpixels each intervening between nearby luminance data Y, therebygenerating plane luminance data Y_(h). The plane luminance data Y_(h)are delivered to the high resolution, plane interpolator.

The high resolution, plane interpolator generates R plane data, G planedata and B plane data on the basis of the plane luminance data Y_(h) andcorrected R, G and B pixel data input thereto. The R, G and B plane dataare fed to the matrix processor. The plane interpolator includesmemories for respectively storing the processed image data and allowingthem to be read out in a nondestructive way. The plane interpolatorcalculates pixel data by reading the pixel data out of the memories.

The matrix processor transforms the R, G and B plane data to luminancedata Y and chrominance data (R-Y) and (B-Y) capable of being displayedon the monitor 42. Specifically, the matrix processor multiplies each ofthe R, G and B plane data by a particular mixture ratio to therebyoutput the luminance data Y and chrominance data (R-Y) and (B-Y). Todetermine mixture ratios, use is made of conventional coefficients. Acutoff frequency containing the frequency bands of the luminance data Yand chrominance data (R-Y) and (B-Y) and not causing aliasing to occuris set in order to execute antialiasing processing. The luminance data Yare fed to an aperture adjusting circuit and have their high frequenciesraised thereby. As a result, the contour of the image is enhanced. Thematrix processor delivers the luminance data Y and chrominance data(R-Y) and (B-Y), or Cr and Cb, (36 a) to the compression/expansioncircuit 38 while delivering them to the monitor 42 on the system bus 16.

As stated above, the signal processor 36 generates the luminance data Yand chrominance data Cr and Cb 36 a by using, among the pixel dataoutput from the photodiodes, the pixel data having close correlation byway of example.

The compression/expansion circuit 38 is made up of a circuit forcompressing image data with the JPEG (Joint Photographic Experts Group)scheme, and a circuit for expanding the compressed image data. Duringrecording, the compression/expansion circuit 38 delivers compressed data38 a to the record/reproduction circuit 40 on the system bus 16 underthe control of the system controller 18. Alternatively, thecompression/expansion circuit 38 may simply pass the data 36 a outputfrom the signal processor 36 therethrough and transfer them to themonitor 42 on the system bus 16 under the control of the systemcontroller 18. During reproduction, the compression/expansion circuit 38receives data 40 a read out of the record/reproduction circuit 40 on thesystem bus 16 and expands them. The expanded data are also fed to themonitor 42 and displayed thereby.

The record/reproduction circuit 40 is made up of a recording section forwriting image data in a recording medium and a reproducing section forreading image data out of the recording medium. The recording medium maybe implemented by a so-called smart medium or similar semiconductormemory, a magnetic disk or an optical disk by way of example. When useis made of a magnetic disk or an optical disk, the record/reproductioncircuit 40 includes a modulator for modulating image data and a head orelectro-magnetic transducer for writing the modulated image data in thedisk.

The monitor 42 displays, under the control of the system controller 18,the luminance data and chrominance data 36 a or the R, G and B data 36 awhile taking account of its screen size and adjusting the timing. Whenthe monitor 42 is implemented by an LCD (Liquid Crystal Display) anddisplays moving pictures, it displays, during preliminary pickup by wayof example, an image halved in the number of photodiodes or pixels inthe horizontal direction.

With the above-described configuration, the camera 10 adequatelycontrols each of preliminary pickup and actual pickup in a particularmanner despite that the image pickup device 30 has high pixel density.Specifically, during preliminary pickup, the camera 10 reads out signalsat high speed in order to rapidly set up exposure conditions for actualpickup to follow. During actual pickup, the camera 10 reads out signalsin such a manner as to obviate color mixture ascribable to the fall oftransfer efficiency that occurs in a low-illumination image area. Thisis successful to enhance the quality of the entire picture withoutregard to illumination.

Reference will be made to FIGS. 2A and 2B for describing the imagepickup device 30 and color filter 28 specifically. FIG. 2A shows apositional relation between the photosensitive array of the image pickupdevice 30 and vertical transfer drive signals V1 through V8 output fromthe driver 22 b. As shown, the image pickup device 30 includesphotosensitive portions 30 a in which photodiodes or photosensitivecells PD are arranged bidimensionally for photoelectrically transduceincident light. Each photodiode PD is shifted from the adjoiningphotodiodes PD in the vertical and horizontal directions, asillustrated. The photosensitive portions 30 a each are formed with anaperture AP in the front thereof. Signal charges are read out of thephotodiodes PD via electrodes EL that are so arranged as to skirt roundthe apertures AP. The signals read out via the electrodes EL aretransferred vertically along vertical transfer registers or verticaltransfer paths VR. Subsequently, the signals are transferredhorizontally, i.e., in the direction perpendicular to the verticaltransfer registers VR along horizontal transfer registers or horizontaltransfer path HR.

The vertical transfer registers VR transfer the signals in accordancewith the vertical transfer drive signals V1 through V8. Specifically,four vertical transfer registers or electrodes VR are assigned to eachphotosensitive portion 30 a. Each photosensitive portion 30 a has tworegions, or registers VR, adjoining each other in the horizontaldirection, i.e., when the photodiodes PD shifted from each other areseen in the horizontal direction. The two adjoining regions refer to twopackets. The horizontal transfer registers HR each simultaneouslyoperate two electrodes as a unit in matching relation to the abovearrangement of the vertical transfer registers VR.

In the illustrative embodiment, the apertures AP are formed in the imagepickup device 30 in a honeycomb pattern, and each has an octagonalshape. While the apertures AP a square lattice configuration, the cruxis that the apertures AP be capable of enhancing sensitivity andproviding the vertical transfer registers VR with the same width tothereby prevent transfer efficiency from decreasing. The apertures APmay therefore have a polygonal shape, a square lattice shape rotated by45 degrees (e.g. rhombic) or even a hexagonal shape.

As also shown in FIG. 2A, the color filter 28 has color filter segmentsCF each covering one of the apertures AP. The filter segments CF eachare positioned just in front of a particular photodiode PD. Assume thatthe distance between nearby photodiodes PD is a pixel pitch PP. Then,the apertures AP are arranged in rows and columns that are shifted bythe pixel pitch PP horizontally and vertically, as illustrated. When theapertures AP are polygonal, they may be more densely arranged inmatching relation to the polygon. In such a case, apertures AP in rowsand columns may be shifted from each other by one-half of the pixelpitch PP. For example, when the apertures AP are octagonal, as shown inFIG. 2A, they may be shifted by one-half of the pixel pitch PP (|PP|/2)in both of the horizontal and vertical directions. In this manner, thedense arrangement of the apertures AP depends on the shape of eachaperture AP.

In FIG. 2A, the photodiodes PD arranged in a vertical stripe at the leftend of the image pickup device 30 and labeled R is assumed to be anodd-numbered column. As indicated by dots in FIG. 2A, the vertical drivesignals V1, V3, V5 and V7 each containing field shift gate pulses areapplied to particular electrodes EL.

How the camera 10 operates when the shutter release button is pressed toits half-stroke position assigned to preliminary pickup will bedescribed hereinafter. This operation is unique to the illustrativeembodiment. FIG. 2A shows the image pickup device 30 in a preliminarypickup condition wherein signals are read out at high speed. First,before the condition of FIG. 2A occurs, signal charges are read out ofthe photodiodes PD arranged on odd-numbered columns. For this purpose,the timing signal generator 22 a included in the timing signal feedingsection 22 feeds field gate pulses only to the vertical drive signals V1and V5. The drive signals V1 and V5 with the field gate pulsessuperposed thereon are applied to the electrodes EL, so that field shiftgates associated with the electrodes EL are turned on. The driver 22 bsends four-phase vertical drive signals to the vertical transfer pathsVR in order to transfer the signal charges along the vertical transferpaths VR. FIG. 2A shows a condition wherein the signal charges have beentransferred from the vertical transfer paths VR to the horizontaltransfer path HR by one packet of the paths VR. As shown in FIG. 2B,horizontal drive signals H1 through H4 are sequentially fed to thepackets of the horizontal transfer path HR.

By the vertical transfer, the signal charges are positioned on thehorizontal transfer path HR in a relation of “,_,_,R,_,_,_,B,_,_,_,G,_,_,_, . . .”. It is to be noted that the symbol “_” is representativeof a vacant packet where a signal charge is absent. The horizontaltransfer path HR has a four-electrode structure similarly, as statedearlier. As shown in FIG. 2A, the signal charges are present in everyfourth packet. It will therefore be seen that the transfer of the signalcharges in a direction A shown in FIG. 2B is effected at a rateequivalent to one available with four-phase drive. More specifically,because four-phase drive usually transfers signal charges by oneelectrode (packet) in one-fourth of a single period, signal charges canbe transferred by four electrodes (packets) in a single period.Therefore, two-phase drive originally effected, but at a rate equivalentto one available with four-phase drive, successfully doubles thetransfer rate without the reading frequency being varied.

The above-described relation is shown in FIG. 3 in terms of the timingsfor feeding the horizontal drive signals H1 through H4 and the resultingshifting of potential wells with respect to time. As shown in FIG. 3,part (a), the horizontal drive signals H1 and H2 are identical with eachother and fed at the same timing in order to double the region of thesame phase. This is also true with the horizontal drive signals H3 andH4. Consequently, a potential well is formed over each two packets,causing the signal charges to be sequentially transferred on a packetbasis. It is therefore possible to read out the signal charges input tothe horizontal transfer path HR at a doubled transfer rate simply byvarying the timings of the horizontal drive signals, while maintainingtwo-phase drive and having a four-electrode structure.

For example, assume that the image pickup device 30 has 1,280 pixels inthe horizontal direction. Then, during preliminary pickup, signalcharges are read out of only 640 pixels at a doubled reading speed. Theunique arrangement of the filter segments CF obviates color mixturedespite that the pixels are mixed in the vertical direction. Bycombining such vertical pixel mixture and the horizontally reduced driveparticular to the illustrative embodiment, it is possible to promoteaccurate calculations for AE/AF in, e.g., a dark scene.

To read signal charges out of only even-numbered columns, an arrangementmay be made such that the timing signal generator 22 a delivers verticaldrive timing signals and field shift gate pulses to the driver 22 b andcauses the driver 22 b to superpose them. In such a case, the driver 22b should only feed the superposed vertical drive signals V3 and V7 tothe image pickup device 30 (see FIG. 2A).

FIG. 3, part (b), shows potential wells formed in the horizontaltransfer path HR. As shown, barriers exist between nearby signal chargesand allow the signal charges to be read out without color mixture.

While the foregoing description has concentrated on preliminary pickup,actual pickup with the camera 10 is also apt to bring about thedefective transfer of a low-illumination region due to the current trendtoward high horizontal drive frequency and low drive voltage.Consequently, color mixture occurs in the low-illumination region anddegrades image quality, i.e., color reproducibility. Such degradation ofimage quality is aggravated due to the increasing demand for high pixeldensity and low power consumption.

In light of the above, at the time of actual pickup, signal charges areread out of each of the odd-numbered columns and even-numbered columnsof photodiodes PD, FIG. 2A, at a particular timing in the same manner asduring preliminary pickup. This obviates the degradation of imagequality ascribable to color mixture and occurring in, e.g., a dark scene(pickup with low illumination). The term “particular timing” mentionedabove refers to, e.g., a particular field or a particular frame. Whensuch intervals are applied to the read-out of signal charges duringactual pickup, the signal charges can be read out with a margin withrespect to time without any deterioration.

For comparison, another arrangement for reading signal charges out ofthe image pickup device 30 will be described with reference to FIGS. 4Aand 4B. As shown in FIG. 4A, the image pickup device 30 is identicalwith the image pickup of FIG. 2A except that the filter segments of thecolor filter are arranged in, e.g., a G square, RB full checker pattern.While this pattern is also an octagonal pattern, it has G filtersegments arranged in a square lattice and has R or B filter segmentsarranged at the centers of the square lattice, i.e., in an RB fullchecker pattern. Signal charges are read out of the photodiodes PD byprogressive scanning. The field shift gate pulses generated by thetiming signal generator 22 a are superposed on the vertical drive timingsignals so as to produce the vertical drive signals V1, V3, V5 and V7.To read signal charges out of the photodiodes PD, the driver 22 b feedsthe vertical drive signals V1, V3, V5 and V7 to the electrodes or fieldshift gates EL. As a result, signal charges are output from both of theodd and even-numbered columns to the vertical transfer paths VR at thesame time.

Assume that in the configuration shown in FIG. 4A the signal charges aresimply read out of only the odd-numbered columns or the even-numberedcolumns at a time, as in the illustrative embodiment. Then, only thecolors R and B or the color G is read out line by line in the horizontaldirection because of the G square, RB full checker pattern. That is, thecolors R, G and B do not appear together on a single line, obstructingadequate interpolation at the signal processing stage. However, becausethe photodiodes PD are shifted in the above color filter pattern, signalcharges can be simultaneously read out of two lines without colormixture and output to the horizontal transfer path HR, as shown in FIG.4A. As shown in FIG. 4B, the horizontal transfer path HR has afour-electrode structure and transfers the signal charges by using asingle packet as a barrier.

As shown in FIG. 5, part (a), the arrangement performs two-phase drivein transferring signal charges on the horizontal transfer path HR.Specifically, the horizontal drive signals H1 and H3 are fed in onephase while the horizontal drive signals H2 and H4 are fed in the otherphase. The horizontal drive signals H1 and H3 generate potential wells,as shown at the top of FIG. 5, part (b). Subsequently, the horizontaldrive signals H2 and H4 are fed and cause the potential wells to move byone packet, as shown at the button of FIG. 5, part (b). Such a procedureis repeated to read two lines of signal charges as a single line. Thiskind of signal reading scheme, however, does not give consideration topixel reduction in the horizontal direction, i.e., reads out signalcharges in the same manner as during actual pickup of the illustrativeembodiment. The conventional scheme therefore needs, in the event ofhigh-speed reading, a period of time two times longer than the period oftime particular to the illustrative embodiment. The long reading timeascribable to priority given to image quality is not desirable from theoperation standpoint. For example, if the preliminary pickup is slow,then the operator cannot set up pickup conditions at a desired timingbefore actual pickup and must, in the worst case, simply wait withoutany shot.

As stated above, in the illustrative embodiment, the camera 10 includesthe octagonal color filter 28 in which three primary colors R, G and Beach are arranged in a vertical stripe. The timing signal feedingsection 22 feeds drive signals assigned to preliminary pickup to theimage pickup device 30. Specifically, during preliminary pickup, signalcharges are read out of only the odd-numbered columns or theeven-numbered columns to thereby effect pixel reduction. When the signalcharges are transferred along the horizontal transfer path HR, thehorizontal drive signals are fed such that each two packets form thesame potential. The signal charges can therefore be read out bytwo-phase drive as if they were read out by four-phase drive, withoutthe reading frequency being varied. This doubles the horizontal transferrate and therefore prevents the operator from, e.g., missing a shutterchance at the time of actual pickup despite that the image pickup device30 has high pixel density. The illustrative embodiment therefore freesthe operator from uneasiness and insures high image quality.

In summary, in accordance with the present invention, a solid-stateimage pickup apparatus includes a color filter having an R, G and Bvertical stripe pattern. During preliminary pickup, a signal feedingsection feeds particular drive signals for reading signal charges out ofonly odd-numbered columns or even-numbered columns. As a result, thesignal charges or image data reduced to, e.g., one-half in thehorizontal direction are transferred along a horizontal transfer path.The signal feeding section feeds horizontal drive signals adjusted intiming to the horizontal transfer path, causing the above image data tobe read out without varying reading frequency. This doubles thehorizontal transfer rate and therefore prevents the operator from, e.g.,missing a shutter chance at the time of actual pickup despite that animage pickup section has high pixel density. The present inventiontherefore frees the operator from uneasiness and insures high imagequality.

The entire disclosure of Japanese patent application No. 253887/1999filed Sep. 8, 1999 including the specification, claims, accompanyingdrawings and abstract of the disclosure is incorporated herein byreference in its entirety.

While the present invention has been described with reference to theillustrative embodiment, it is not to be restricted by the embodiment.It is to be appreciated that those skilled in the art can change ormodify the embodiment without departing from the scope and spirit of thepresent invention.

1. A solid-state image pickup apparatus comprising: an image pickupsection; and a signal feeding section; said image pickup sectioncomprising: photosensitive cells for photoelectrically transducingincident light representative of a scene, said photosensitive cellsbeing arranged bidimensionally in such position that each of saidphotosensitive cells is shifted in position substantially halfway fromadjoining ones of said photosensitive cells in a horizontal and avertical direction; a color filter having R (red), G (green) and B(blue) color filter segments for separating colors of the incidentlight, each of the color filter segments being positioned in front of aparticular one of said photosensitive cells in a direction of theincident light and being arranged in a vertical stripe pattern in whichthe segments of a same color form a column in the vertical direction;first transfer electrodes, each being assigned to a particular one ofsaid photosensitive cells, for reading out a signal charge generated bysaid particular photosensitive cell, second transfer electrodes assignedto vertical transfer paths, and third transfer electrodes assigned to ahorizontal transfer path substantially perpendicular to the verticaltransfer paths for forming at least one vacant packet between packetsholding the signal charges transferred from said vertical transferpaths; and control circuitry for sequentially performing preliminarypickup and actual pickup, which reads all of the signal charges out ofsaid photosensitive cells, and executing digital signal processing withsignals resultant from the signal charges read out; second signalfeeding section feeding transfer timing signals for transferring thesignal charges generated by ones of said photosensitive cells which arepositioned on odd or even-numbered ones of the columns to the verticaltransfer paths via said first transfer electrodes associated with saidphotosensitive cells on odd-or even-numbered lines, vertical drivesignals for transferring the signal charges along said vertical transferpaths toward said horizontal transfer path, and horizontal drive signalsadjusted in timing for transferring the signal charges along saidhorizontal transfer path while maintaining a color of the signalcharges, wherein each photosensitive cell is assigned four verticaltransfer registers the vertical transfer registers grouped in pairs inthe vertical direction and formed on both sides of the photosensitivecell in the horizontal direction, where adjacent pairs assigned toadjacent photosensitive cells shifted in position are adjoined to formthe vertical transfer paths.
 2. An apparatus in accordance with claim 1,wherein in the event of the preliminary pickup said signal feedingsection output said horizontal drive signals such that a well is formedin each packet of said horizontal transfer path adjoining a packetstoring the individual signal charge at the same time as a well formedin said packet storing said individual signal charge.
 3. An apparatus inaccordance with claim 1, wherein said signal feeding section outputssaid horizontal drive signals such that a range of said horizontaltransfer path driven in a same phase and derived from an electrodestructure of said horizontal transfer path is doubled.
 4. An apparatusin accordance with claim 3, wherein when said horizontal transfer pathhas a four electrode structure, said signal feeding section outputs saidhorizontal drive signals such that two phases are combined into a singlephase.
 5. A method of reading signal charges generated by photosensitivecells, which are arranged bidimensionally in such positions that each ofsaid photosensitive cells is shifted in position substantially halfwayfrom adjoining ones of said photosensitive cells in a horizontal and avertical direction for photoelectrically transducing incident light ofparticular separated color representative of a scene, in a particularmanner for preliminary pickup and actual pickup, which reads all of thesignal charges out of said photosensitive cells for recording the signalcharges, said method comprising the steps of: (a) positioning in frontof said photosensitive cells in a direction of the incident light acolor filter, which has color filter segments of three primary colors R,G and B each for separating colors of the incident light and arranged ina vertical stripe pattern in which the segments of same color form acolumn in the vertical direction, and forming transfer electrodes, eachof which is assigned to a particular one of the photosensitive cells forreading out a signal charge generated by said particular photosensitivecell, said transfer electrodes respectively contacting saidphotosensitive cells, wherein each photosensitive cell is assigned fourvertical transfer registers, the vertical transfer registers grouped inpairs in the vertical direction and formed on both sides of thephotosensitive cell in the horizontal direction, where adjacent pairsassigned to adjacent photosensitive cells shifted in position areadjoined to form the vertical transfer paths; (b) generating drivesignals for reading out the signal charges generated by saidphotosensitive cells and representative of an image picked up; (c)rendering conductive, during the preliminary pickup, the transferelectrodes associated with ones of the photosensitive cells which arepositioned on odd or even-numbered lines in response to the drivesignals to reduce pixels in the horizontal direction by verticalthinning, where each of said photosensitive cells is shifted in positionfrom adjoining ones of said photosensitive cells in a horizontal and avertical direction; (d) transferring the signal charges read out in saidstep (c) in the vertical direction in response to the drive signals; and(e) transferring the signal charges having transferred in said step (d)in the horizontal direction perpendicular to said vertical directionwith a timing of the drive signals being adjusted.
 6. A method inaccordance with claim 5, wherein said step (b) comprises the step (f) ofgenerating, in the event of the preliminary pickup, horizontal drivesignals such that a well is formed in each packet horizontally adjoininga packet storing an individual signal charge at the same time as a wellformed in said packet storing said individual signal charge.
 7. A methodin accordance with claim 5, wherein said step (e) comprises the step (g)of generating said drive signals such that a range of a same phase isdoubled in the horizontal direction.
 8. A method in accordance withclaim 7, wherein, when four-phase drive signals are used for usualhorizontal transfer, said step (e) comprises the step (h) of generatingsaid drive signals such that two phases are combined into a singlephase.